Transparent polarized light-emitting device

CROSS-REFERENCE TO RELATED APPLICATION

0001This application claims the benefit of U.S. Provisional Application No. 61/136,965, filed Oct. 17, 2008 and titled TRANSPARENT POLARIZED LIGHT-EMITTING DEVICE, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

0002This disclosure relates to a transparent polarized light-emitting device.

BACKGROUND

0003Organic light-emitting diodes (OLEDs) are optoelectronic devices made by placing a layer of organic material between two electrodes. When a voltage potential is applied to the electrodes and current is injected through the organic material, visible light is emitted. Due to the high power efficiency, low cost of manufacture, and durability of OLEDs, and the fact that they are lightweight, OLEDs are often used to create visual displays for portable electronic devices.

SUMMARY

0004In one general aspect, a transparent directional polarized light-emitting device includes a transparent anode and a transparent cathode, a radiation-emitting layer between the anode and the cathode, an optically active reflective layer with a reflection band that matches a chirality and at least partially encompasses a wavelength band of radiation emitted from the radiation-emitting layer, the optically active light blocking layer located on a side of the radiation-emitting layer, and a transparent substrate adjacent to the optically active reflective layer.

0005Implementations may include one or more of the following features. The radiation-emitting layer may include an organic light-emitting layer. The radiation-emitting layer may include an inorganic light-emitting layer. The inorganic light-emitting layer may include a quantum dot emitter. The device may include a hole transport layer located between the anode and the radiation-emitting layer. The device may include an electron transport layer located between the radiation-emitting layer and the cathode. The device may include an electron tunneling barrier layer located between the cathode and the electron transport layer. The device may include an electron tunneling barrier adjacent to the radiation-emitting layer. The organic light-emitting layer may include a non-racemic compound of chiral organic light emitting molecules. The organic light-emitting layer may include glass-forming chiral nematic liquid crystals (GLCs) that are embedded with organic light-emitting dopants, and the organic light emitting layer may emits chiral light.

0006The transparent cathode may be a spin polarized electrode. The transparent cathode may be one of a ferromagnetic electrode and a half-metallic electrode. The transparent anode may be a spin polarized electrode. The optically active reflective layer may include morphologically stable glass-forming chiral nematic liquid crystals (GLCs). The optically active reflective layer may include a cholesteric liquid crystal.

0007The device may include a second optically active reflective layer adjacent to the optically active reflective layer, and a reflection band of the second optically active reflective layer may have an opposite chirality to that of the optically active reflective layer and may at least partially encompasses a wavelength band of radiation emitted from the radiation-emitting layer. The second optically active reflective layer may include morphologically stable glass-forming chiral nematic liquid crystals (GLCs). The transparent anode and the transparent cathode transmit may visible light. The optically active reflective layer may include a sculptured thin film. The light-emitting layer may include a chiral material.

0008In another general aspect, a polarized light-emitting device is fabricated by a method that includes forming a radiation-emitting layer. The radiation-emitting layer includes a radiation-emitting material that emits radiation having a wavelength included in an emission wavelength band. The radiation-emitting material is disposed between a transparent anode and a transparent cathode. An optically active reflective layer is disposed adjacent to the radiation-emitting layer. The optically active reflective layer includes glass-forming chiral nematic liquid crystals (GLC), and the optically active reflective layer is configured to reflect radiation having a wavelength included in a reflection wavelength band of the optically active reflective layer. The reflection wavelength band of the optically active reflective layer is adjusted to at least partially encompass the emission wavelength band of the radiation-emitting layer.

0009Implementations may include one or more of the following features. The radiation-emitting material may include an organic light-emitting layer. Adjusting the reflection wavelength band of the optically active reflective layer may include heating the glass-forming chiral nematic liquid crystals above a glass transition temperature (Tg) and near a critical point (Tc) of the glass-forming chiral nematic liquid crystals. The optically active reflective layer may be irradiated with electromagnetic radiation for a time duration sufficient to alter the reflection wavelength band of the optically active reflective layer to at least partially encompass an emission wavelength band of the light-emitting layer. The optically active reflective layer may cooled to a temperature below (Tg). Irradiating the optically active reflective layer may include irradiating the optically active reflective layer with ultraviolet (UV) radiation.

0010Adjusting the reflection wavelength band of the optically active reflective layer may include adjusting a molecular composition of the glass-forming chiral nematic liquid crystals. Adjusting the reflection wavelength band of the optically active reflective layer may result in changing a width of the reflection wavelength band. The radiation-emitting material may include an inorganic light-emitting layer. The optically active reflective layer may include a first GLC film made of a right-handed glassy cholesteric material, and a second GLC film made of a left-handed glassy cholesteric material, the second GLC film being adjacent to the first GLC film. Adjusting the reflection wavelength band of the optically active reflective layer may include adjusting a molecular ratio of the right-handed glassy cholesteric material to the left-handed glassy cholesteric material. The molecular composition of both the first GLC film and the second GLC film may be adjusted to adjust the reflection band of the optically active reflective layer.

0011In some implementations, a second optically active reflective layer may be deposited on the optically active reflective layer. The second optically active reflective layer and the optically active reflective layer have opposite chirality. The reflection wavelength band of the second optically active reflective layer may be adjusted to at least partially encompass the emission wavelength band of the light-emitting layer. The optically active reflective layers may be deposited consecutively, the reflection wavelength band of the second optically active reflective layer may be adjusted on a separate substrate, and the optically active reflective layer may be bonded to one side of the transparent polarized light emitting device after the reflection wavelength band of the second optically active reflective layer is adjusted.

0012In some implementations, the optically active layer is deposited on a transparent substrate. The transparent substrate may be located between the optically active reflective layer and the light-emitting layer.

0013Implementations of the described techniques may include hardware, a method or process, a device, an apparatus, or a system. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

0014<figref idref="DRAWINGS">FIGS. 1 and 2</figref> show examples of a directionally biased light-emitting device.

0015<figref idref="DRAWINGS">FIG. 3</figref> shows an example of a directionally biased light-emitting device that includes two optically active reflective layers.

0016<figref idref="DRAWINGS">FIGS. 4A and 4B</figref> show examples of a directionally biased light-emitting device that includes one optically active reflective layer.

0017<figref idref="DRAWINGS">FIGS. 5A and 5B</figref> show examples of directionally biased light-emitting devices that include an organic light-emitting diode (OLED) stack.

0018<figref idref="DRAWINGS">FIG. 6A</figref> shows an example of a directionally biased light-emitting device that includes an organic light-emitting diode (OLED) stack.

0019<figref idref="DRAWINGS">FIG. 6B</figref> shows an illustration of emission characteristics from the device shown in <figref idref="DRAWINGS">FIG. 6A</figref>.

0020<figref idref="DRAWINGS">FIG. 7</figref> shows an example process for fabricating a directionally biased light emitting device.

0021<figref idref="DRAWINGS">FIGS. 8A-8C</figref> illustrate an example process of pixilating a phototunable liquid crystal.

0022<figref idref="DRAWINGS">FIGS. 9A-11A</figref> each show a perspective view of an example directionally biased light emitting device.

0023<figref idref="DRAWINGS">FIGS. 9B-11B</figref> respectively show a cross-sectional view of the directionally biased light emitting devices shown in <figref idref="DRAWINGS">FIGS. 9A-11A</figref>.

0024<figref idref="DRAWINGS">FIG. 12</figref> shows a stacked transparent light-emitting device.

0025<figref idref="DRAWINGS">FIG. 13</figref> shows another stacked transparent light-emitting device.

DETAILED DESCRIPTION

0026A transparent device that emits radiation from one side, or primarily from one side, is described. In particular, an optically active reflective material is placed on a transparent electroluminescence device such that radiation emitted from a light-emitting layer in the device emanates only from one side of the device, or primarily from one side of the device, while ambient light is transmitted by both sides of the device. The device emits chiral radiation having a range of wavelengths, and a reflection band of the optically active reflective material is tuned to match both the helicity and the wavelength of the radiation emitted from the device such that the optically active reflective material reflects the emitted radiation. In this manner, the transparent electroluminescence device may be directionally biased such that emitted radiation emanates from only one side of the device, or primarily from one side of the device, rather than from both sides of the device.

0027The disclosed techniques relate to a particular application of organic light-emitting diode (OLED) technology. In particular, the disclosed techniques relate to transparent OLEDs (TOLEDs) that exploit the spin-polarization and the wavelength of emitted light to achieve unidirectional emission. The devices are transparent in that the devices are made from one or more materials that are at least partially transmissive to radiation incident upon the materials. Such TOLEDs may be referred to as transparent organic unidirectional polarized light-emitting diodes (TOUPLEDs). TOUPLEDs may be incorporated into or coated on to windshields to, for example, allow a driver to see information displayed on the windshield without the information being visible from the other side of the windshield. Because the TOUPLED is transparent to ambient light, ambient light passes through the windshield. Similarly, TOUPLED technology may be utilized on helmets, specifically, military combat helmets or other visualization instruments that include a visor or eyepiece. With such an arrangement, the user of the helmet may view information displayed on one side of the visor while also being able to see through the visor because ambient light enters the visor. For example, the TOUPLED may be mounted on a visor of a military helmet such that a solider using the helmet may view tactical information displayed on the inside part of a helmet visor while the displayed tactical information would not be viewable from the side of the visor facing the environment (which is the side on which the optically active reflective layer is mounted). However, because the TOUPLED is made from materials that are at least partially transparent to ambient light, ambient light continues to pass through the visor.

0028Referring to <figref idref="DRAWINGS">FIG. 1</figref>, an example of a directionally biased transparent light-emitting device <b>100</b> is shown. The light-emitting device <b>100</b> includes a light-emitting layer <b>1</b>, an optically active reflective layer <b>2</b>, and a transparent substrate <b>4</b>. The light-emitting layer <b>1</b> is disposed between a first electrode <b>5</b> and a second electrode <b>6</b>. The first electrode <b>5</b> may be a transparent anode, and the second electrode <b>6</b> may be a transparent cathode. The first electrode <b>5</b> and the second electrode <b>6</b> are transparent to the wavelengths of the radiation emitted from the light-emitting layer <b>1</b> to allow emission of radiation from the device <b>100</b>. Additionally, the first electrode <b>5</b> and the second electrode <b>6</b> may be transparent to ambient light such that ambient light may pass through the device <b>100</b>. Although in the example shown in <figref idref="DRAWINGS">FIG. 1</figref>, the first electrode <b>5</b> is located at a top <b>7</b> of the light-emitting layer <b>1</b>, and the second electrode <b>6</b> is located at a bottom <b>8</b> of the light-emitting layer <b>1</b>, in other examples, the first electrode <b>5</b> and the second electrode <b>6</b> may be arranged in the opposite configuration.

0029When a positive bias is applied across the first electrode <b>5</b> and the second electrode <b>6</b>, the anode injects holes (positive charge carriers) into the light-emitting layer <b>1</b>, and the cathode injects electrons (negative charge carriers) into the light-emitting layer <b>1</b>. The holes and electrons recombine in the light-emitting layer <b>1</b> and generate excitons that lead to luminescence. In this manner, the light-emitting layer <b>1</b> emits radiation, preferably in the form of visible light. As discussed in more detail below, the radiation emitted from the light-emitting layer <b>1</b> has a wavelength and a chirality (e.g., the radiation is circularly polarized and has a left-handed or a right-handed orientation or the radiation is elliptically polarized and has a left-handed or a right-handed orientation).

0030As discussed in more detail below, the optically active reflective layer <b>2</b> blocks the radiation emitted from the light-emitting layer <b>1</b> by reflecting the emitted radiation back towards the top <b>7</b> of the light-emitting layer <b>1</b> and into a light-emission envelope <b>9</b> that is on one side of the device <b>100</b>. In particular, the optically active reflective layer <b>2</b> has a reflective band that encompasses, at least partially, the wavelengths of the radiation emitted from the light-emitting layer <b>1</b>. The reflective band of the optically active reflective layer <b>2</b> is the band of wavelengths that are not transmitted by the optically active reflective layer <b>2</b>. Additionally, the optically active reflective layer <b>2</b> has a chirality that matches the chirality of the radiation emitted from the light-emitting layer <b>2</b>.

0031The optically active reflective layer <b>2</b> may be considered to match the chirality and the wavelength of the radiation emitted from the light-emitting layer <b>2</b>. By matching the chirality and the wavelength, the index of refraction of the optically active reflective layer <b>2</b> may be tuned, or otherwise modified, such that the wavelength of the radiation emitted from the light-emitting layer <b>2</b> is centered on the reflection band of the of the optically active reflective layer <b>2</b> and that the optically active reflective layer <b>2</b> reflects radiation having a helical polarization. Radiation having a helical polarization is radiation that has either is elliptically polarized or circularly polarized and has either a right-handed or left-handed helicity, or chirality. An elliptically or circularly polarized electromagnetic wave in which the electric field vector, observed in a fixed plane normal to the direction of propagation while looking in the direction of propagation, rotates in a left-handed direction, i.e., in a counterclockwise direction, and the direction of propagation is the same as the forward direction of a left-handed screw when being screwed into a fixed nut.

0032In some implementations, matching the chirality and the wavelength may include tuning the index of refraction of the optically active reflective layer <b>2</b> such that the optically active reflective layer <b>2</b> has a spectral reflection band that includes at least a portion of the wavelengths of the radiation emitted from the light-emitting layer <b>2</b>. In these implementations, the optically active reflective layer <b>2</b> may have a reflection band that is centered on the emission band of the emitted radiation, but that is not necessarily the case.

0033The optically active reflective layer <b>2</b> also may be referred to as an optically active blocking layer or an optically active filter layer. In the example shown in <figref idref="DRAWINGS">FIG. 1</figref>, radiation emitted from the light-emitting layer <b>1</b> exits the directionally biased transparent light-emitting device <b>100</b> through the top <b>7</b> rather than through the bottom <b>8</b> of the light-emitting layer <b>1</b>. However, in other examples, the optically active reflective layer <b>2</b> may be located on the side of the top <b>7</b> of the light-emitting layer <b>1</b> such that radiation emitted from the light-emitting layer <b>1</b> exits the device <b>100</b> through the substrate <b>4</b>. Thus, the device <b>100</b> may be a top-emitting transparent device or a bottom-emitting transparent device.

0034In one implementation, the transparent light-emitting device <b>100</b> is a transparent organic unidirectional polarized light-emitting device (TOUPLED). In this implementation, the first electrode <b>5</b> is a transparent anode, and the light-emitting layer <b>1</b> is a chiral organic molecule based light emitting layer (which may be referred to as a chiral organic light emitting layer). As discussed below with respect to <figref idref="DRAWINGS">FIGS. 5A and 5B</figref>, the TOUPLED also may include an electron tunneling barrier layer, a spin polarized cathode (which may be referred to as a spin-cathode), the transparent substrate <b>4</b> and, an optically active light filter layer (which may be referred to as an optically active reflective layer) tuned to the wavelength and chirality of the emitted light. In one example, the chirality of the optically active reflective layer may be right handed such that right-handed circularly polarized light emitted from the light emitting device is reflected by the optically active reflective layer <b>2</b>. In other implementations, the light-emitting layer may be made from, or may include, any light-emitting material that emits radiation having chiral components (e.g., light that is not linearly polarized).

0035In another implementation, the light-emitting layer <b>1</b> may be an achiral luminophore. An achiral luminophore is a light emitter that does not necessarily emit chiral radiation but may be configured, structured, or arranged to emit chiral radiation. For example, in this implementation, the light-emitting layer <b>1</b> may be an inorganic quantum dot emitter, and the quantum dot emitter may be arranged in a chiral matrix that produces chiral radiation. In these implementations, the quantum dot emitters are deposited as a single monolayer. Depositing the quantum dot emitters as a single monolayer may help localize and, thus, control the formation and relaxation of excitons.

0036In other implementations, any transparent OLED layer that is transparent and does not interfere with the chirality of the emitted and blocked radiation may be used. A material that is not optically active, or is weakly optically active, does not impart a polarization on radiation passing through the material. Thus, such a material may be used as the transparent OLED layer. Materials that may be used as a transparent OLED layer includes glass and ITO. In implementations that use spin-injectors, any transparent OLED layer that minimizes interference with the charge-spin life with the charge-spin life time or the chirality of the emitted and blocked radiation may be used.

0037Referring to <figref idref="DRAWINGS">FIG. 2</figref>, an example of a directionally biased transparent light-emitting device <b>200</b> is shown. The device <b>200</b> includes a light-emitting layer <b>201</b>, a optically active reflective layer <b>202</b>, a transparent substrate <b>204</b>, a first electrode <b>205</b>, and a second electrode <b>206</b>. The device <b>200</b> may be similar to the device <b>100</b> discussed above with respect to <figref idref="DRAWINGS">FIG. 1</figref>, except the transparent substrate <b>204</b> is disposed between the optically active reflective layer <b>202</b> and the light-emitting layer <b>201</b>. Similar to the device <b>100</b>, the device <b>200</b> emits polarized radiation into an emission envelope <b>209</b> on one side of the device <b>200</b>.

0038Referring to <figref idref="DRAWINGS">FIG. 3</figref>, an example of a directionally biased light-emitting device <b>300</b> that includes two light-blocking layers, a right-handed optically active layer <b>310</b> and a left-handed optically active layer <b>320</b>, is shown. The device <b>300</b> also includes a light-emitting layer <b>330</b>, a transparent substrate <b>340</b>, a first electrode <b>350</b>, and a second electrode <b>365</b>. As discussed in more detail below with respect to <figref idref="DRAWINGS">FIGS. 5A and 5B</figref>, radiation emitted from the light-emitting layer <b>330</b> may be chiral radiation (e.g., circularly or elliptically polarized light). Depending on the configuration of the light-emitting device <b>300</b>, the chiral radiation may include approximately equal amounts of chiral light with right-handed helicity and chiral light with left-handed helicity, or the emitted chiral radiation may include primarily chiral light with right-handed helicity or primarily chiral light with left-handed helicity.

0039In the example shown in <figref idref="DRAWINGS">FIG. 3</figref>, the light-emitting layer <b>330</b> emits radiation that includes chiral light with left-handed helicity and chiral light with right-handed helicity. Chiral light <b>355</b> with right-handed helicity is reflected from the optically active reflective layer <b>310</b>, and the chiral light <b>360</b> with left-handed helicity is reflected from the optically active reflective layer <b>320</b>. Thus, the radiation emitted from the bottom <b>370</b> of the light-emitting layer <b>330</b> is reflected through the top <b>380</b> of the device <b>300</b> rather than exiting device through both the bottom <b>370</b> and the top <b>380</b>. Because the chirality of helicallypolarized light conserves orientation upon reflection off of an optically active material, but reverses orientation upon reflection off of a non-optically active material, the chiral light <b>360</b> is reflected as light with left-handed helicity, and the chiral light <b>355</b> is reflected as light with right-handed helicity.

0040Referring to <figref idref="DRAWINGS">FIGS. 4A and 4B</figref>, examples of a directionally biased light-emitting device <b>400</b> that includes one optically active reflective layer <b>405</b> is shown. The device <b>400</b> includes a light-emitting layer <b>410</b> formed on a substrate <b>420</b>. The light-emitting layer <b>410</b> emits radiation <b>440</b> that is circularly polarized and has a right-handed helicity. As discussed with respect to <figref idref="DRAWINGS">FIGS. 5A and 5B</figref>, the helicity of the radiation emitted from the light-emitting layer <b>410</b> may be controlled by, for example, introducing a population of spin up electrons into the light-emitting layer <b>410</b>. As shown in the example of <figref idref="DRAWINGS">FIG. 4A</figref>, the radiation <b>440</b> emitted from the light-emitting layer <b>410</b>, which has right-handed helicity, is reflected from the optically active reflective layer <b>405</b> and is emitted from a top <b>450</b> of the device <b>400</b>. The optically active reflective layer <b>405</b> has a reflection band that has a right-handed chirality, and, thus, because the radiation <b>440</b> is chiral light with right-handed helicity, the optically active reflective layer <b>405</b> reflects the radiation <b>440</b>.

0041Referring to <figref idref="DRAWINGS">FIG. 4B</figref>, the behavior of the device <b>400</b> in the presence of circularly polarized light with left-handed helicity and right-handed helicity is illustrated. Circularly polarized radiation <b>460</b> with right-handed helicity emanates from the device <b>400</b> and is reflected from the optically active reflective layer <b>405</b> as circularly polarized radiation <b>460</b> with right-handed helicity. The polarized radiation <b>470</b> is reflected from the optically active reflective layer <b>405</b> because the chirality of the reflective band of the layer <b>405</b> is also right-handed. The radiation <b>470</b> is also reflected off of an object <b>465</b>, changes orientation upon reflection to radiation <b>480</b>, which has left-handed helicity. Because the radiation <b>480</b> has left-handed helicity, the chirality of the reflective band of the optically active layer <b>405</b> does not match the chirality of the radiation <b>480</b>. Thus, the radiation <b>480</b> passes through the optically active reflective layer <b>405</b>.

0042As discussed above, a TOUPLED may include one or more of an anode, an organic light emitting layer, a cathode, a substrate, and an optically active light blocking layer. In some implementations, the TOUPLED also includes one or more of an electron transport layer (ETL), an electron tunneling barrier layer (TBL), and a hole transporting layer (HTL). In some implementations, certain materials/substances may function as one discrete element described above and herein or may act as more than one described above and herein. For example, a particular material/substance may be used as an anode and possess certain characteristics of a hole transport layer.

0043Referring to <figref idref="DRAWINGS">FIGS. 5A and 5B</figref>, examples of directionally biased light-emitting devices <b>500</b>A and <b>500</b>B that include an organic light-emitting diode (OLED) stack are shown. Referring to <figref idref="DRAWINGS">FIG. 5A</figref>, the device <b>500</b>A includes an OLED stack <b>20</b>, a substrate <b>24</b>, a right-handed optically active reflective layer <b>28</b>, and a left-handed optically active reflective layer <b>29</b>. The OLED stack <b>20</b> includes a cathode <b>21</b>, electron tunneling barrier layer <b>27</b>, electron transport layer <b>25</b>, light-emitting layer <b>22</b>, hole transport layer <b>26</b>, and anode <b>23</b>. Anode <b>23</b> is adjacent to the substrate <b>24</b>. Referring to <figref idref="DRAWINGS">FIG. 5B</figref>, the device <b>500</b>B includes an OLED stack <b>30</b>, a substrate <b>34</b>, and an optically active reflective layer <b>38</b>. The OLED stack <b>30</b> of the TOUPLED may include a cathode <b>31</b>, electron tunneling barrier layer <b>37</b>, electron transport layer (ETL) <b>35</b>, light-emitting layer <b>32</b>, hole transport layer <b>36</b>, and anode <b>33</b>. The anode <b>33</b> is adjacent to the substrate <b>34</b>.

0044The directionally biased light-emitting devices <b>500</b>A and <b>500</b>B may be TOUPLEDs. TOUPLEDs may be considered as a series of adjacent layers consecutively deposited on a substrate. The substrate may be the substrate <b>4</b>, the substrate <b>204</b>, the substrate <b>340</b>, the substrate <b>24</b> or the substrate <b>34</b> discussed above. Techniques for depositing layers on the substrate include, for example, chemical vapor deposition, physical vapor deposition, sputtering, thermal evaporation, e-beam deposition, vacuum deposition, spin-coating, and a modification of inkjet printer technology. The techniques for depositing layers on the substrate also may be used to introduce or “dope” additional compounds into a layer that has been deposited. For example, during fabrication of a TOUPLED, an electron transport layer (ETL), such as the electron transport layer <b>25</b> or the electron transport layer <b>35</b> discussed with respect to <figref idref="DRAWINGS">FIGS. 5A and 5B</figref>, may be deposited and doped with a metal either by depositing the ETL on an ultra-thin layer of lithium or by depositing the ultra-thin layer of lithium on the ETL. Based on the thicknesses of the layers prepared in this manner, the lithium may diffuse entirely, from either direction, throughout the ETL, thus forming a degenerately-doped ETL. A layer of lithium could also be deposited on both sides of the ETL, or the lithium could be co-deposited with the ETL. The lithium layer may be deposited such that the layer is about 0.5 to 1.0 nm thick.

0045The substrate on which the TOUPLED is fabricated is a material that is transparent to the chirality and wavelength of the radiation emitted from the TOUPLED. For example, the substrate may be glass and/or plastic. Polymer films made from, for example, polyvinylene chloride (PVC), polyethylene terephthalate (PET), polyether sulfone (PES), polyethylene naphthalate (PEN), polycarbonate (PC), nylon, polyether ether ketone (PEEK), polysulfone (PSF), polyether imide (PEI), polyarylate (PAR) and polybutylene terephthalate (PBT) may be used as plastic substrates.

0046The TOUPLED may include an anode, which injects positively charged carriers (“holes”) into a light-emitting layer. In some implementations, as mentioned above, depending on the particular type of material/substance utilized as an anode, the anode also may transport holes into the light-emitting layer. The anode may be made from, for example, transparent indium tin oxide (ITO) or In₂O₃:SnO₂. The anode may be, for example, the anode <b>23</b> or the anode <b>33</b> discussed above with respect to <figref idref="DRAWINGS">FIGS. 5A and 5B</figref> respectively. The light-emitting layer may be the light-emitting layer <b>22</b> or the light-emitting layer <b>32</b>.

0047The TOUPLEDs also includes a cathode, such as the cathode <b>21</b> or the cathode <b>31</b>. Cathodes inject negatively charged carriers or electrons into the light-emitting layer. In some implementations, depending on the particular type of material/substance utilized as a cathode, the cathode also transports electrons into the light-emitting layer. Cathode layers may be deposited using, for example, dc sputtering/cylindrical target deposition. ITO and Indium Zinc Oxide (IZO) are two examples of a conductive material for use in manufacturing transparent cathode layers. Subsequent cathode layers may include a transparent, metallic or non-metallic materials and that serve to improve quantum efficiency of the emitting device, electron injection, minimize work function, and as a protective buffer layer facilitating the deposition of the ITO on predeposited organic layers; a transparent metal-doped cathode layer that may also function as an exciton blocking layer and/or as a hole blocking layer; or a transparent, metallic or non-metallic cathode layer followed by an electron selective layer made of a material that possesses different conductivities for up and down electron spins. Suitable materials for use in transparent cathodes to facilitate electron transport and injection may include, but are not limited to, lithium fluoride (LiF), aluminum (Al), lithium-doped aluminum (Li:Al), magnesium-doped silver (Mg:Ag), bathocuproine (BCP) (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), cesium carbonate (CsCO3), lithium-doped bathocuproine (LiBCP) or cesium-doped phenyldipyrenylphosphine oxide (CsPOP_y2).

0048In order to control the helicity of the chiral light emitted from the TOUPLED, the population of electrons having a spin up quantum spin state as compared to the population of electrons having a spin down quantum spin state may be controlled. Electrons exist in two quantum spin states, spin up and spin down, which are associated with equivalent units of angular momentum values of opposite sign. A normally distributed population of electrons is a mixture containing an equal number of electrons in the spin up state and in the spin down state. When a normally distributed population of electrons recombines with holes in a layer of organic light emitting molecules, chiral light (e.g., circularly and/or elliptically polarized light) is produced. The light emitted is approximately an equal mixture of light with right handed helicity (RH) and light with left handed helicity (LH).

0049In some implementations, however, the TOUPLED may utilize electrons in a single spin state. When the electrons in a single spin state recombine with holes in the TOUPLED, due to quantum spin-selection rules, the emitted chiral light has a single handedness (helicity) relative to the emitter molecule orientation. The helicity of the emitted light is measured with respect to the emitter molecule's axis of magnetic alignment and the sign is a function of the spin state of the injected electrons and holes. For example, when electrons in the spin-up state recombine with holes, chiral light with right-handed helicity is emitted in a forward direction with respect to an aligning magnetic field. When electrons in the spin down state recombine with holes, chiral light with left-handed helicity is emitted in a forward direction with respect to an aligning magnetic field.

0050Spin polarized electrons may be produced by, for example, spin filtration via tunneling and spin polarization via a magnetized injector. Spin filtration via tunneling utilizes an electron tunneling barrier layer (TBL) located either adjacent to the cathode or sandwiched between two electron transport layers, one of which is adjacent to the cathode. Electrons in the spin up state have greater momentum than electrons in the spin down state. The greater momentum of electrons in the spin up state allows these electrons to tunnel through the TBL, while electrons in the spin down state are unable to pass through the TBL. Therefore, the TBL enriches the current flowing in the light-emitting layer with electrons in the spin up state. The population of spin up electrons radiatively recombines with holes in the light-emitting layer, and, thus, the light-emitting layer emits chiral light with right handed helicity. Spin tunneling filtration may yield an electron population with nearly 100% spin up electrons. Thus, the emitted radiation is nearly 100% right-handed polarized radiation. The TBL may be made from, for example, Eu_xO_y(x>>y), which is selected for its ability to participate in large exchange splitting in the conduction band (on the order of 0.6 eV), and because of its high degree of transparency. Other materials having a high degree of transparency and the ability of participate in exchange splitting, such as magnesium monoxide and ITO, may be used. Electrons carry different magnetic momentum depending on the spin state of the electron. Certain materials participate in exchange splitting, and in these materials, electrons in the spin-up state (which have a higher momentum that electrons in the spin-down state) have a higher probability of tunneling through the material. The larger the exchange splitting, the more effectively the material discriminates between spin-up and spin-down electrons. Thus, in materials having relatively large exchange splitting, spin-up electrons have a higher probability of tunneling through the material and, as a result, more spin-up electrons pass through. As a result, a spin-polarized current is generated.

0051In some implementations, electrons in the spin up state may be produced via a magnetized injector. A magnetic electron injection cathode, such as chromium doped indium tin oxide, forms spin-up polarized electrons that are injected into the light-emitting layer. The radiative recombination of electrons in the spin-up state with holes results in the emission of chiral light with right-handed helicity. The electron-spin selective cathode may be made from, for example, chromium doped indium tin oxide (Cr:ITO); chromium doped indium oxide (Cr:IO); any transparent half metal (Mo, Zr, Nb, Ru, Tc doped with K₂S (about 5% doped)); Zr, Tc, and Ru doped with K₂O (about 5% doped); or Zr, Nb, and Ru doped with K₂Se, K₂Te, or Rb₂S; any transparent Heusler alloy; any compound from a class of materials known to be half-metallic and having the formula X₂YZ, where X and Y are transition elements (groups IB to VIIIB on the periodic table) and Z is a group III, IV, or V element.

0052In some implementations, a magnetized injector may be used in combination with an electron tunneling barrier layer to achieve a purer spin-polarized current at a higher ambient temperature than either the spin filtration or the magnetized injector may achieve singly. The magnetized injector may be used to supply a pre-spin polarized current (e.g., spin-up) to the tunnel barrier that in turn filters out any remaining electrons in the spin down state. Polarized electrons in the spin up state also may be produced by hybrid spin injecting tunneling filters. Like their electron counterparts, holes may be considered as existing in two separate quantum spin states. Thus, chiral light of a single helicity may be produced by the radiative recombination of electrons with spin polarized holes. Chiral light of a single helicity also may be produced by the radiative recombination of spin polarized electrons with spin polarized holes.

0053<figref idref="DRAWINGS">FIG. 6A</figref> shows an example of a directionally biased light-emitting device that includes an organic light-emitting diode (OLED) stack. The example device <b>600</b> shown in <figref idref="DRAWINGS">FIG. 6A</figref> is a TOUPLED that includes an organic light-emitting layer (OLEL) <b>602</b> that is transparent. The OLEL <b>602</b> includes a cathode <b>604</b>, an electron injection layer <b>606</b>, an electron transport layer <b>608</b>, an organic light-emitting layer <b>610</b>, a hole transport layer <b>612</b>, and an anode <b>614</b>. An optically active reflective layer may be disposed on either the cathode or the anode of the stack. In the example shown in <figref idref="DRAWINGS">FIG. 6A</figref>, an optically active reflective layer <b>630</b> is disposed on the cathode <b>604</b>.

0054In the example shown in <figref idref="DRAWINGS">FIG. 6A</figref>, the anode <b>614</b> includes a conductive anode of ITO and glass. The ITO layer is approximately forty-two nanometers (42-nm) thick. The light-emitting layers <b>602</b> also include a inter-layer electrical short reduction layer <b>613</b> made from a layer of molybdenum oxide (MoO3) that is about 20-nm thick, and the hole transport layer <b>612</b>, which in this example includes a layer of N,N′di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB) that is about 55-nm thick. The light-emitting layer <b>610</b> is made of Alq3+C6 and is about 60-nm thick, and the electron transport layer <b>608</b> is about 40-nm thick and is made of 4,7-Diphenyl-1,10-phenanthroline (Bphen). The electron injection layer <b>606</b> is about 0.5-nm thick and made of lithium fluoride (LiF). In the example of <figref idref="DRAWINGS">FIG. 6A</figref>, the cathode <b>604</b> include ITO and aluminum (Al). The ITO layer is about 65-nm thick, and the aluminum layer is about 100 nm thick. The presence of the aluminum layer allows the ITO to be sputtered, or otherwise, applied to the electron injection layer <b>606</b>.

0055In another implementation, the cathode may include a conductive cathode of ITO and glass, an electron injection layer of cesium carbonate (CsCO3), an electron transport layer of Bphen, a light-emitting layer of Alq3+C6, a hole transport layer of MoO3 and NPB, and an anode of silver (Ag) and ITO. The silver portion of the anode may be a thin layer of silver through which light passes, and the silver acts as a protective layer that allows the ITO to be sputtered onto the hole transport layer.

0056The device <b>600</b> also includes the optically active reflective layers <b>630</b>. The optically active reflective layers <b>630</b> include a layer of glass <b>632</b>, and an alignment coating <b>634</b> that is about 30-40-nm thick and buffed horizontally. A layer of the alignment coating <b>634</b> is placed on both sides of a right-handed GLC <b>636</b>, which is about 8-μm thick, and a layer of glass <b>638</b> is disposed on the opposite side of the GLC <b>636</b>. An index matching adhesive <b>640</b> is disposed on the layer of glass <b>638</b>, and an alignment coating <b>646</b> that is buffed vertically and is about 30 to 40-nm thick is disposed on both sides of a left-handed GLC <b>648</b> that is about 8-μm thick. A layer of glass <b>652</b> and an index matching adhesive layer <b>654</b> are also included in the optically active reflective layers <b>630</b>. In the example shown in <figref idref="DRAWINGS">FIG. 6A</figref>, the right-handed GLC and the left-handed GLC are both tuned to have a reflection band about 75-nm wide and centered at 525-nm.

0057In either of these implementations, the optically active layers <b>630</b> may be adjacent to the cathode <b>604</b> or to the anode <b>614</b>. In the example of <figref idref="DRAWINGS">FIG. 6A</figref>, the optically active layers <b>630</b> are adjacent to the cathode <b>604</b> and the directionally biased light from the device <b>600</b> is emitted from the bottom <b>650</b> of the device.

0058The layer thicknesses may be other than specified in the example of <figref idref="DRAWINGS">FIG. 6A</figref>. In some implementations, the hole transport layer <b>612</b> may be a thickness between 5-nm and 100-nm, the organic light-emitting layer <b>610</b> may have a thickness between 10-nm to several hundred nm, the electron transport layer <b>608</b> may have a thickness between 10-nm to several hundred nm, and the thin-metal electron injection layer <b>606</b> (which is aluminum in the example of <figref idref="DRAWINGS">FIG. 6A</figref>), may have a thickness between 10-nm and several hundred nm.

0059<figref idref="DRAWINGS">FIG. 6B</figref> illustrates emission characteristics of the device <b>600</b> that is shown in <figref idref="DRAWINGS">FIG. 6A</figref>. The emission characteristics include a curve <b>690</b> and a curve <b>695</b>, each of which represent intensity as a function of the wavelength of radiation emitted from the device <b>600</b>. The curve <b>690</b> shows emissions from the bottom of the device <b>600</b>, and the curve <b>695</b> shows emissions from the top of the device <b>600</b>. As seen in <figref idref="DRAWINGS">FIG. 6B</figref>, the device <b>600</b> is directionally biased such that the intensity of emissions from the bottom of the device <b>600</b> is greater than the emission from the top of the device <b>600</b>. The emissions from the top of the device <b>600</b> are mainly attributable to leakage from the device <b>600</b>. However, the emissions from the bottom of the device <b>600</b> are caused by reflections of the light from the light emitting layers <b>602</b> off of the optically active layers <b>630</b>. Thus, the emissions from the bottom of the device <b>600</b> are significantly greater in intensity than the emissions from the top of the device <b>600</b>, and the emissions from the bottom of the device <b>600</b> are centered on a wavelength of about 525-nm due to the tuning of the reflection bands of the GLC layers <b>636</b> and <b>648</b> that are included in the optically active reflective layers <b>630</b>.

0060In some implementations, the TOUPLED also may include additional layers disposed between the anode and the cathode, each layer having different compositions and performing different functions. Such materials should be selected for their charge mobility characteristics to generate a smooth energy-level transitions (ionization potentials) between successive layer interfaces where unrestricted charge transport is desired or to generate energy barriers where localization of charge carrier recombination is desired. Materials may be small molecules or polymers. For example, the TOUPLED may include an electron transport layer (ETL), such as the electron transport layer <b>35</b>. The ETL may efficiently disperse the injected current of negative charge carriers (electrons) across the surface of the layer, and the ETL provides a homogenous current at the boundary of the ETL and the layer on the side of the ETL opposite from the cathode. The ETL may also serve as a positive charge carrier (hole) blocking layer to promote the likelihood and localization of charge carrier recombination in the light emitting layer. A spin-polarized electron transport layer may improve the probability that the spin polarized state of the injected electrons is conserved. Suitable ETL materials include, but are not limited to 4,7-Diphenyl-1,10-phenanthroline (Bphen), 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), or Tris-(8-hydroxyquinolinato)aluminum (Alq₃).

0061In other implementations, a hole transport layer (HTL), such as the hole transport layer <b>36</b>, may be provided to efficiently disperse the positive charge carriers (holes) across the HTL so that a homogenous current (hole) is provided to the surface of the layer adjacent to the HTL, which may be the light-emitting layer. The HTL may also serve as a negative charge carrier (electron) blocking layer to promote the likelihood and localization of charge carrier recombination in the light emitting layer. One or more HTL layers may be used in succession. The HTL may be made from a host of materials including but not limited to N,N′di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), or 4,4′-bis[N(1-napthyl)-N-phenylamino]biphenyl (alpha-NPD) (NPD), 1,3,5-Tris(diphenylamino)benzene 97% (TDAB), or from the TDATA family such as 4,4′,4″-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA) as small molecule examples, or Poly(2-vinylnaphthalene) as a polymer example. Dopant materials may be added to the HTL to improve device lifetime and efficiency. For instance, NPB may be doped with molybdenum oxide (MoO3) to reduce the hole injection barrier, improve interfacial stability, and suppress crystallization of the HTL.

0062In some implementations, the materials/substances that function as the ETL or as the HTL may include the same materials that are incorporated into the light-emitting layer to produce the electroluminescent emission. If the HTL or ETL function as the emissive layer (e.g., the light-emitting layer) of such a device, then the TOUPLED may be referred to as having a single heterostructure. Alternatively, a TOUPLED, having a separate layer of electroluminescent material included between the HTL and ETL, may be referred to as having a double heterostructure. Thus, a heterostructure for producing electroluminescence may be fabricated as a single heterostructure or as a double heterostructure.

0063In some implementations, one or more buffer layers may be inserted between successive layers to reduce the abrupt differential barrier height between successive layer work-function.

0064The material properties of the light-emitting layer determine the wavelength and, hence, the color of the radiation emitted from the OLED. Through selecting differing organic solids for the light-emitting layer with a material such as coumarin 6 (C6), or through doping the organic solid used to make the light-emitting layer, the color of the radiation emitted may be varied. In some implementations, individual TOUPLED stacks include light-emitting layers that emit light of a particular color, and in other implementations, a TOUPLED includes multiple light-emitting layers that each emit light of different colors. TOUPLED light emitting materials with narrow band emission (saturated color) should be selected Suitable material for the light emitting layer include, but are not limited to Tris-(8-hydroxyquinolinato)aluminum (Alq₃), Bis-(8-hydroxyquinolinato)zinc (Znq), Tris(1,10-phenanthroline)ruthenium(II) chloride hydrate, as small molecule examples, or Poly(9,9-di-(2-ethylhexyl)-9H-fluorene-2,7-vinylene) as a polymer example.

0065Furthermore, in some implementations, the wavelength of the radiation emitted by the organic light emitting layer (OLEL) may be modified by addition of fluorescent and/or phosphorescent materials that absorb the light emitted by the light-emitting layer and re-emit radiation of longer wavelength. In some implementations, the color of the emitted radiation may be altered by placing a colored or photoluminescent film between the TOUPLED and the observer.

0066The TOUPLED also includes an optically active reflective layer, such as the optically active reflective layer <b>2</b>, the optically active reflective layer <b>202</b>, the optically active reflective layers <b>405</b> and <b>420</b>, the optically active reflective layer <b>28</b> and <b>29</b>, or the optically active reflective layer <b>38</b>. The optically active reflective area may be an optically-active chiral-light blocking layer (OA-LBL). Materials suitable for use as OA-LBLs include, for example, dichroic materials, organic compounds containing asymmetric carbon atoms, and from inorganic compounds such as glass-forming chiral nematic liquid crystals (GLC), and chiral dielectric sculptured thin film wavelength selective reflectors. Furthermore, the layers that function as OA-LBL may be deposited using methods similar to those used to deposit the other layers of a TOUPLED. Sculptured thin films are fabricated using a technique that involves controlling the motion of the substrate on which the film is fabricated during the fabrication process. Typically, fabrication of the sculptured thin film involves computerized control of the rotation of the substrate about two axis during the deposition process.

0067In one implementation, the OA-LBL may include a GLC layer which is a cholesteric thin film including a helical stack of quasinematic liquid crystal layers. The optical properties of the GLC film are determined to a large degree by the chirality (i.e. Right- or Left-handedness) and helical pitch length. The chirality of the GLC film is determined by the rotational direction of the cumulative nematic director twisting which results from the rotation of each successive quasinematic liquid crystal layer about the intended optical axis of the film. The helical pitch length the distance required to complete a 360-degree rotation of the optical director. A cholesteric liquid crystal film may be made of a helical stack of quasi-pneumatic layers, and the handedness (right-handedness or left-handedness) describes the direction in which twisting of the nematic director occurs from one layer to the next. The helical pitch length is the distance along the direction of propagation of radiation through the layers over which the director rotates 360°.

0068Cholesteric liquid crystals may be derived from nematic liquid crystals that have been doped with very low concentrations of chiral dopants, and the cholesteric pitch of the cholesteric phases is sensitive to structural modifications of the chiral dopant. Thus, the initial helical pitch is largely determined by the selection of a particular chiral dopant, and the reflection band of the GLC layer may be set by selecting a particular dopant molecule without necessarily performing subsequent photomodulation on the GLC layer. The ability of the GLC film to selectively reflect a given wavelength is governed a relationship between the helical pitch length and the extraordinary and ordinary refractive indices of the quasi-nematic layers. The differential between these extraordinary and ordinary refractive indices determines the overall optical birefringence of the GLC film, which, in turn, determines the width of the selective reflection wavelength band. The wavelengths associated with this selective reflection band may be altered by modifying the GLC chemical composition. Additionally or alternatively, the reflection band may be tuned by, for example, photomodulation of the GLC film or by altering or adjusting the molecular ratio of the GLC film. In some implementations, the reflection band may be adjusted using both photomodulation and adjustment of the molecular ratio by, for example, adjusting the molecular ratio of the materials in the GLC film and then photomodulating the GLC film.

0069In some implementations, the reflection band of the GLC layer may be considered to act as an optical notch filter that has a reflection band set (or tuned) by adjusting a molecular ratio between the materials from which the GLC film is made. For example, the GLC optical notch filter may have two adjacent single-handed GLC films, with each film having a chirality that is opposite from the chirality of the other film. In this implementation, each GLC film includes an appropriate ratio of right-handed (R) and left-handed (S) glassy cholesteric material such as, for example, 2NICH-R and 2N1CH-S, respectively. A ratio of the left-handed glassy cholesteric material to the right-handed glassy cholesteric material may be adjusted to tune the reflection band of the GLC film. This ratio may be referred to as the GLC ratio and may be considered to be a molecular ratio of the right-handed (R) glassy choloesteric material to the left-handed (S) glassy cholesteric material. For example, a GLC ratio of S-to-R molecules of 81:19 results in an enantiomeric excess of “S” molecules that yields a single left-handed film in a particular wavelength range. The opposite GLC ratio (S-to-R of 19:81) results in an enantiomeric excess of “R” molecules that yields a single right-handed film at the same, or almost the same, wavelength range. Adjusting the GLC ratio shifts the reflection band of the GLC film, and may thus be considered to tune the GLC film. Additionally, the molecular composition of the glassy cholesteric material may be modified to adjust the width of the optical notch (e.g., the spectral width of the reflection band). An example structure of a GLC molecule from U.S. Pat. No. 7,001,648, which is herein incorporated by reference in its entirety, as shown below.

0070<chemistry id="CHEM-US-00001" num="00001"><img file="US8253153B2_D0001.tif" /></chemistry>

0071In implementations having multiple GLC films, the GLC films may be adjacent to each other by overlapping, or partially overlapping, each other such that radiation that is incident on one of the GLC films and propagates through the GLC film is also incident on the other GLC film. The adjacent GLC films may overlap by making contact with each other, or the GLC films may be positioned close to each other, without necessarily touching each other, such that radiation passes from one film to the other. The GLC films may be aligned such that the optical director of one GLC film is perpendicular to the optical director of the other GLC film.

0072In some implementations, the GLC reflection band wavelength may be increased or decreased by completing a photomodulation process on a deposited GLC film. In some implementations, the photomodulation process includes heating the GLC thin film to a point above the glass transition temperature of the film (Tg) followed by a period of irradiation with ultraviolet (UV) radiation. The glass transition temperature of the film depends on the chemical composition of the film. The GLC thin film also may be heated to a temperature near a critical temperature (Tc) of the film. For example, a GLC with Tg of 68° C. and Tc of 134° C. may be heated to 120° C. (thus the GLC thin film is heated to a temperature of 14° C. from the Tc). The heating is followed by a period of UV irradiation with, for example, UV radiation having a wavelength of 334 nm and an intensity of 70 mW/cm².

0073The longer the exposure time to the UV radiation, the longer the resulting nematic liquid crystal helical pitch length, and hence the longer the selective reflection band wavelength of the GLC thin film. The irradiation time is dependant on the initial (unmodulated) reflection band, but the irradiation time is a time duration that is sufficient to alter the reflection wavelength band of the GLC thin film. The closer the initial reflection band is to the final desired reflection band, the shorter the required irradiation. Typically, within the visible spectrum, irradiation times may last from tens of seconds, to tens of minutes. For example, the irradiation time to shift the reflection band from 400 nm to 550 nm may be about 10 minutes, whereas the band shift from 400 nm to 750 nm may be about 40 minutes. The radiation used to irradiate the GLC film may be unpolarized UV light. UV light is used if only a GLC optical notch filters (stacked left- and right-handed GLC filters) are being simultaneously photomodulated (e.g., tuned).

0074The film is then cooled to a point below (Tg; typically room temperature) at which point the attained selective reflection wavelength becomes frozen in the solid state of the GLC thin film.

0075In some GLC materials the photomodulation process is reversible, where heating of the GLC thin film with a predetermined selective reflection band above (Tg) followed by irradiation of the film with a shorter wavelength than the selective reflection band for a sufficient period of time decreases the helical pitch length of the nematic liquid crystal, thereby decreasing the wavelength of the GLC selective reflection band. Subsequent cooling to a point below Tg will freeze the reflection wavelength in the solid state of the GLC thin film in the TOUPLED application, in one implementation, a GLC OA-LBL layer of a given chirality (left- or right-handed) is selected to match the chirality of the helically-polarized light emitting layer and is deposited on the exposed side of the TOUPLED substrate. The GLC layer is subsequently photomodulated (e.g., tuned) to encompass the wavelength band emitted by the organic light-emitting layer. The photomodulation process may be accomplished by using either an external radiation source or light emitted by the TOUPLED light emitting layer itself.

0076In another implementation, the TOUPLED light emitting layer includes a light emitting layer that achieves a less than ideal degree of helical polarized emission. In this implementation, a GLC OA-LBL layer of right-handed chirality and a GLC OA-LBL layer of left-handed chirality are deposited successively on the exposed side of the TOUPLED substrate. Following deposition, both layers are subjected to an identical photomodulation process to tune the GLC OA-LBL layers to encompass the wavelength band emitted by the organic light-emitting layer. The photomodulation process may be accomplished by using either an external radiation source or light emitted by the TOUPLED light emitting layer itself. Chiral light with a right handed helicity may be reflected by the right-handed OA-LBL and chiral light with left handed helicity may be reflected by the left-handed OA-LBL. Electrons in the spin-up state produce a chiral light wave with right handed helicity, that in turn may be reflected by the right-handed OA-LBL. The result is a transparent device that emits chiral light only from that side of the device that does not have the OA-LBL layer or layers.

0077Ambient light is randomly polarized and includes a combination of waveforms polarized in all orientations. The majority of ambient light is of a wavelength that is outside of the OA-LBL stop band (which also may be referred to as the reflection band) and is therefore transmitted by the OA-LBL layer. The relatively small portion of ambient light that falls into the OA-LBL stop band and that also matches the chirality of the OA-LBL is reflected. Chiral light produced within the TOUPLED from a population of electrons in the spin up state, for example, may be emitted from the top of the device and absorbed or reflected by the OA-LBL on the bottom of the device. In contrast, the device is equally transparent to ambient light passing through the device in either direction.

0078Referring to <figref idref="DRAWINGS">FIG. 7</figref>, an example process <b>700</b> for fabricating a directionally biased light emitting device is shown. The polarized light emitting device may be a TOUPLED as discussed above. A radiation-emitting layer is formed (<b>710</b>). The radiation-emitting layer includes a radiation-emitting material is disposed between a transparent anode and a transparent cathode. The radiation-emitting material has a spectral emission band such that all radiation, or almost all radiation, emitted from the radiation-emitting material has a wavelength that falls within the emission band. The emission band of the radiation-emitting material depends on properties, such as index of refraction, of the material from which the radiation-emitting layer is made. The radiation-emitting material may be a light-emitting layer made from an organic material such as, for example, Alq3+C6. The radiation-emitting material may be a light-emitting layer such as the light-emitting layers <b>7</b>, <b>201</b>, <b>330</b>, <b>410</b>, <b>22</b>, and <b>32</b> discussed above.

0079An optically active reflective layer is deposited adjacent to the radiation-emitting layer (<b>720</b>). Thus, the optically active reflective layer may be on the anode side or the cathode side of the radiation-emitting layer. The optically active reflective layer may include glass-forming chiral nematic liquid crystals, and the optically active reflective layer has a spectral reflection band that may be referred to as the reflection wavelength band. The optically active reflective layer reflects radiation that has a wavelength within the reflection band. The optically active reflection layer transmits little, if any, radiation that has a wavelength in the reflection band and possesses the same chirality as the optically active reflection layer (because the optically active reflection layer reflects such radiation). The optically active reflective layer may be deposited on a transparent substrate such as the transparent substrates <b>4</b>, <b>204</b>, <b>340</b>, <b>420</b>, <b>24</b>, and <b>34</b> discussed above. The transparent substrate may be located between the optically active layer and the radiation-emitting layer, but that is not necessarily the case. The optically active reflective layer may include a first glassy liquid crystal (GLC) film made of a right-handed material and a second GLC film made of a left-handed material that is adjacent to the first GLC film.

0080The reflection wavelength band of the optically active reflective layer is adjusted to at least partially encompass the emission wavelength band of the radiation-emitting layer (<b>730</b>). Thus, after the reflection wavelength band of the optically active layer is adjusted, the optically active layer reflects radiation that is emitted from the radiation-emitting layer. However, because the layers of the device are transparent to ambient light, a user of the device is able to see through the device. Thus, as discussed below, the device may be used for in-line-of-sight illumination applications. As discussed above, adjusting the optically active reflection layer may include photomodulating the optically active reflection layer, adjusting the molecular composition of the optically active layer, or photomodulating the optically active layer after adjusting the molecular composition of the optically active layer.

0081A second optically active layer may be deposited on the optically active layer deposited in (<b>720</b>). The second optically active layer has a chirality that is opposite that of the optically active layer deposited earlier. Thus, if the earlier-deposited optically active layer has a left-handed chirality, the second optically active layer has a right-handed chirality. The reflection wavelength band of the second optically active layer may be adjusted separately from the first optically active reflection band and adjusted on a separate substrate. Once the reflection band of the second optically active layer is adjusted, the second optically active layer may be bonded to one side of the TOUPLED device.

0082The directionally biased transparent light-emitting devices discussed above such as devices <b>200</b>, <b>300</b>, <b>400</b>, <b>500</b>A, <b>500</b>B, and <b>600</b> may be used in an electronic display, in-line-of-sight illumination applications, and in dual-sided transparent display applications. For example, the devices may be used in a non-transparent flat panel display and standard applications of flat panel displays, and the devices may be used in transparent flat panel electronic displays including active matrix-based displays having a thin film transistor (TFT) backplane, passive matrix-based displays, monochrome displays, or full-color displays. To use the device in an electronic display, the GLC layer may be pixilated such that portions of the GLC layer are individually addressable.

0083To use the light-emitting device in an monochrome display, a single optically active layer (e.g., a GLC or sculptured thin film) that is shared by all, or multiple, pixels that make up the display) may be used. For full-color displays in which sets of red, green, and blue pixels are arranged in a spatial pattern and used to make a multi-color display, the reflection band of various portions of the GLC layer may be selectively tuned by exposing the various portions of the GLC layer to photomodulation. In this manner, the GLC may be considered to be pixilated.

0084<figref idref="DRAWINGS">FIGS. 8A-8C</figref> illustrate a process for pixilating a GLC, or other phototunable optically active material.

0085Referring to <figref idref="DRAWINGS">FIG. 8A</figref>, a red-light emitting layer <b>810</b>, a green-light emitting layer <b>812</b>, and a blue-light emitting layer <b>814</b> are deposited on a glass substrate <b>820</b>. Each of the red-light emitting layer <b>810</b>, the green-light emitting layer <b>812</b>, and the blue-light emitting layer <b>814</b> may be OLEDs that emit, respectively, red light, green light, and blue light. A phototunable optically active reflective layer <b>825</b> is disposed on the emitting layers <b>810</b>, <b>812</b>, and <b>814</b>.

0086Referring to <figref idref="DRAWINGS">FIG. 8B</figref>, a shadow mask <b>830</b> having openings <b>832</b> and <b>834</b> is positioned above the phototunable optically active reflective layer <b>825</b>. The openings <b>832</b> and <b>834</b> are sized to correspond to a size of a pixel to be formed on the optically active reflection layer <b>825</b>. UV radiation <b>840</b> is directed towards the shadow mask <b>825</b> and passes through the openings <b>832</b> and <b>834</b> to irradiate portions <b>826</b> and <b>827</b>, respectively, of the optically active reflecting layer <b>825</b>. The portions <b>826</b> and <b>827</b> are exposed to the UV radiation <b>840</b> for a sufficient amount of time to tune the reflection band of the portions <b>826</b> and <b>827</b> such that the portions <b>826</b> and <b>827</b> reflect red light having a helicity that is the same as that of the layer <b>825</b>. Subsequently, the shadow mask <b>830</b> may be repositioned (not shown) relative to the optically active layer <b>825</b> such that other portions of the optically active reflective layer <b>825</b> are exposed to the UV radiation <b>840</b>. As a result, the reflection band of each of these portions is tuned to reflect red, green, or blue light depending on the time duration of the exposure the UV radiation <b>840</b>.

0087Referring to <figref idref="DRAWINGS">FIG. 8C</figref>, the localized irradiation of the optically active reflecting layer <b>825</b> has been repeated to produce, in addition to portions <b>826</b> and <b>827</b>, portions <b>832</b>, which reflect green light, and portions <b>834</b>, which reflect blue light. Thus, the optically active reflecting layer <b>825</b> has been pixilated into portions (which may be pixels) that reflect red light, portions that reflect green light, and portions that reflect blue light. As a result, light emitted from the light-emitting layers <b>810</b>, <b>812</b>, and <b>814</b> is reflected from, respectively, the portions <b>832</b>, <b>827</b>, and <b>834</b> of the optically active reflective layer <b>825</b> and passes through the transparent substrate <b>820</b>.

0088Thus, <figref idref="DRAWINGS">FIGS. 8A-8C</figref> illustrate a process for pixilating an optically active reflective layer, such as a GLC. However, for applications in which maximization of transmission of ambient light is not a priority, instead of pixilating an optically active reflective layer into individual pixels or portions having individually tailored reflection bands, the optically active layer may be deposited in a continuous strip, strips, or sheet that spans the entire height and/or width, or a portion of the height or width, of the emitting device. Configurations that use a single, non-pixilated optically active reflective layer may be simpler and/or less expensive to manufacture than an implementation that includes a pixilated GLC.

0089<figref idref="DRAWINGS">FIGS. 9A-11A</figref> each illustrate a perspective view of an example configuration of a directionally biased light-emitting device that includes multiple single optically active reflective layers. <figref idref="DRAWINGS">FIGS. 9B-11B</figref>, respectively, show a side-view of a vertical cross-section of the configurations shown in <figref idref="DRAWINGS">FIGS. 9A-11A</figref>.

0090Referring to <figref idref="DRAWINGS">FIG. 9A</figref>, a directionally biased light-emitting device <b>910</b> includes pixels <b>915</b>, a transparent substrate <b>920</b>, an optically active layer <b>925</b> with a reflection band tuned to reflect red light, an optically active layer <b>930</b> with a reflection band tuned to reflect green light, and an optically active layer <b>935</b> with a reflection band tuned to reflect blue light. The pixels <b>915</b> may be OLEDs that preferentially emit light from the bottom (the side in contact with the transparent substrate <b>920</b>), and each of the optically active reflective layers <b>925</b>, <b>930</b>, <b>935</b> are shared among all pixels <b>915</b>. The optically active reflection layers <b>925</b>, <b>930</b>, and <b>935</b> may be arranged in a different order, such as shown in <figref idref="DRAWINGS">FIGS. 10A and 11A</figref>.

0091In operation, the pixels <b>915</b> are transparent to light and are, thus, able to emit light from both sides (e.g., from the top and bottom of the pixel). However, the light emitted by the pixels <b>915</b> is preferentially emitted towards the bottom of the pixel (e.g., toward the transparent substrate <b>920</b>). Light that is emitted from the bottom of the pixel passes through the transparent substrate <b>920</b> and is reflected from one of the layers <b>925</b>, <b>930</b>, <b>935</b> that has a reflection band that includes the wavelength and chirality of the light emitted from the pixel. For example, pixel <b>918</b> emits blue light that passes from the bottom of the pixel <b>918</b> through the substrate <b>925</b> and through the red layer <b>925</b>. The light is then reflected from the blue layer <b>930</b> and exits through the top of the pixel <b>918</b> as blue light. The blue light from the pixel <b>918</b> does not reach the green layer <b>935</b>. The pixel <b>919</b> emits green light that from the bottom of the pixel <b>919</b>. The emitted light passes through the red optically active layer <b>925</b> and the blue optically active layer <b>930</b> before the light is reflected from the green optically active layer <b>935</b>. The reflected light is transmitted by the blue optically active layer <b>930</b>, the red optically active layer <b>925</b>, the substrate <b>920</b>, and the pixel <b>919</b> to exit the display <b>910</b>A as green light. The pixel <b>917</b> emits red light into the transparent substrate <b>920</b>, and the light is reflected from the red optically active layer <b>925</b> and exits the device <b>910</b> as red light.

0092Referring to <figref idref="DRAWINGS">FIG. 9B</figref>, a side view of a vertical cross-section of the device <b>910</b> taken along the line “A” is shown. As shown in <figref idref="DRAWINGS">FIG. 9B</figref>, each of the optically active layers <b>925</b>, <b>930</b>, and <b>935</b> are under the pixels <b>917</b>, <b>918</b>, <b>919</b>. Although not shown, the optically active layers <b>925</b>, <b>930</b>, and <b>935</b> are also under the remaining pixels <b>915</b>.

0093Referring to <figref idref="DRAWINGS">FIG. 10A</figref> shows a perspective view of a directionally biased light-emitting device <b>1010</b>. The display device <b>1010</b> is similar to the device <b>910</b> except that the pixels <b>915</b> are deposited on the optically active layers <b>925</b>, <b>930</b>, and <b>935</b> rather than on the transparent substrate <b>920</b>. In the implementation shown in <figref idref="DRAWINGS">FIG. 10A</figref>, the optically active layers <b>925</b>, <b>930</b>, and <b>935</b> are deposited on the transparent substrate <b>920</b>. Thus, in this implementation, light emitted from the bottom of the pixel <b>918</b> is reflected off of the blue optically active layer <b>930</b> without passing through the transparent substrate <b>920</b>. This implementation may result in improved performance (e.g., increased brightness from the device <b>1010</b>) because of, for example, reduction in losses caused by light passing through the substrate <b>920</b> as the light passes from the pixels <b>915</b> to the appropriate optically active layer.

0094<figref idref="DRAWINGS">FIG. 10B</figref> shows a side-view of a vertical cross-section of the device <b>1010</b> taken along the line “B”.

0095<figref idref="DRAWINGS">FIG. 11A</figref> shows a perspective view of a directionally biased light-emitting device <b>1100</b>. In the device <b>1100</b>, the pixels <b>915</b> are deposited on the substrate <b>920</b>, and the optically active reflective layers <b>925</b>, <b>930</b>, <b>935</b> are bonded to the pixels <b>915</b>. In this implementation, the optically active reflective layers are formed on a separate substrate, tuned such that their respective reflection bands reflect red, green, or blue light, and then bonded to the pixels <b>915</b>. In this implementation, light is preferentially emitted from the top of the pixels <b>915</b>, reflects off of the appropriate optically active layer, passes through the pixels <b>915</b> again, and exits the device <b>1100</b> through the transparent substrate <b>920</b>. In such a design, the substrate <b>520</b> may provide protection for the pixels <b>915</b> as well as a platform for deposition. <figref idref="DRAWINGS">FIG. 11B</figref> shows a side view of a vertical cross-section of the device <b>1100</b> taken along the line “C”.

0096In the examples shown in <figref idref="DRAWINGS">FIGS. 9A-11A</figref>, the pixels <b>915</b> are arranged in a delta configuration in which pixels that emit a particular color are arranged along diagonal lines. However, the pixels <b>915</b> may be arranged in other configurations that are suitable for RGB displays. For example, the pixels <b>915</b> may be arranged in a striped pattern that includes alternating contiguous segments of red-light emitters, green-light emitters, and blue-light emitters. In another example, the pixels <b>915</b> may be arranged in a mosaic pattern, or a Pentile® pattern. The Pentile® pattern is available from Samsung Electronics Co., LTD. of the Republic of Korea.

0097Referring to <figref idref="DRAWINGS">FIG. 12</figref>, a stacked transparent light-emitting device is shown. A single pixel, or emitting layer, <b>1200</b> is deposited on a transparent substrate <b>1205</b>. The pixel <b>1200</b> includes a blue-light emitting layer <b>1210</b>, an optically active reflective layer <b>1215</b> that reflects blue light, a green-light emitting layer <b>1220</b>, an optically active reflective layer <b>1225</b> that reflects green light, and a red-light emitting layer <b>1230</b>, an optically active reflective layer <b>1235</b> that reflects red light. In the implementation shown in <figref idref="DRAWINGS">FIG. 12</figref>, each of the light-emitting layers <b>1210</b>, <b>1220</b>, and <b>1230</b> are associated with a transparent anode (not shown) and a transparent cathode (not shown) that controls the emission of light from each of the light-emitting layers.

0098The implementation shown in <figref idref="DRAWINGS">FIG. 12</figref> is different from those shown in <figref idref="DRAWINGS">FIGS. 9A-11A</figref> because each of the light-emitting layers in device <b>1200</b> has a corresponding optically active reflection layer that is adjacent to the emitting layer. Thus, in device <b>1200</b>, light emitted from one of the light-emitting layers is reflected from the adjacent layer instead of traveling through multiple layers as may be the case in the implementations shown in <figref idref="DRAWINGS">FIGS. 9A-11A</figref>. As a result, improved performance (e.g., greater intensity of light emitted from the top of the device <b>1200</b>) may be realized due to the minimization of waveguiding.

0099Referring to <figref idref="DRAWINGS">FIG. 13</figref>, a TOUPLED as a stacked transparent light-emitting device is shown. <figref idref="DRAWINGS">FIG. 13</figref> shows a device <b>1300</b> that is pixilated by selective activation of portions of a stack of light-emitting layers. The device <b>1330</b> includes various light-emitting layers, each of which have a corresponding transparent cathode, and each of which share a common transparent anode. The common anode is divided into separate segments, and activation of a particular segment of the anode and one of the cathodes causes light from the corresponding portion of the light-emitting layers to be emitted.

0100In greater detail, the device <b>1300</b> includes a blue-light emitting layer <b>1310</b>, a green-light emitting layer <b>1320</b>, and a red-light emitting layer <b>1330</b>. A transparent cathode <b>1340</b> contacts the blue-light emitting layer <b>1310</b>, a transparent cathode <b>1350</b> is positioned between the blue-light emitting layer <b>1310</b> and the green-light emitting layer <b>1320</b>, and a transparent cathode <b>1360</b> is positioned between the green-light emitting layer <b>1320</b> and the red-light emitting layer <b>1330</b>. A transparent anode <b>1370</b> is segmented into portions <b>1371</b>-<b>1375</b> such that light is emitted from a particular light-emitting layer, and from a particular portion of the light-emitting layer, depending on which portion of the anode <b>1370</b> is activated. For example, activating the anode portion <b>1372</b> and the cathode <b>1360</b> causes red light <b>1380</b> to be emitted from the red-light emitting layer <b>1330</b>.

0101The device <b>1300</b> also includes optically active reflective layers <b>1385</b>, <b>1390</b>, and <b>1395</b> deposited on a transparent substrate <b>1380</b>. The optically active reflective layers <b>1385</b>, <b>1390</b>, and <b>1395</b> are tuned to reflect, respectively, blue light, green light, and red light. Continuing with the example of the red light <b>1380</b>, the red light <b>1380</b> reflects off of the optically active reflection layer <b>1395</b>, propagates up through the other optically active layers <b>1385</b> and <b>1390</b>, neither of which reflect red light, through the transparent anode <b>1370</b>, the light emitting layers <b>1310</b>, <b>1320</b>, and <b>1330</b>, and the cathodes <b>1340</b>, <b>1360</b>, and <b>1370</b> to exit the device <b>1300</b> through the transparent cathode <b>1370</b>.

0102Thus, <figref idref="DRAWINGS">FIGS. 8A-8C</figref>, <b>9</b>A-<b>11</b>A, <b>9</b>B-<b>11</b>B, <b>12</b>, and <b>13</b> all show a transparent device that includes an optically active reflective layer that causes the device to preferentially emit light from one side of the device. The spectral content of the emitted light is controllable through the tuning of the reflection band of the optically active layer or layers. A user may see through such a device, thus, in addition to displays, in implementations where pixilated optically active reflectors are used or where optically active layers with a single chirality (i.e. left- or right-handed) are used, these devices may be placed in the line-of-sight of a user and used to illuminate a region in view of the user.

0103In addition to being used in the standard displays mentioned above, the transparent light emitting device may be used in transparent head-up displays (HUDs) for the display of information or for use in virtual or augmented reality applications. A head-up display may be a transparent display that presents visual data in the line-of-sight of a user such that the user may view the data without having to look away from their usual viewpoint. The TOUPLED discussed above may be used in a variety of head-up displays. For example, the TOUPLED may be used in vehicular HUD and general illumination applications such as applications that display information on a vehicle's windshield (e.g., aircraft, automobile, motorcycle), automobile signal lights, air traffic control, and visual landing aid lighting.

0104The TOUPLED also may be used in helmet-mounted HUD applications such as aircraft pilot visor HUDs, combat solider embedded helmet HUDs, embedded protective helmet visor HUDs used by, for example, search and rescue workers, and visors used by athletes, such as football helmet visors. Additionally, the TOUPLED may be used in architectural HUD applications, such as digital signage (e.g. billboards, “spectacular” or architectural displays on buildings), retail displays used for narrowcasting, and window-mounted or embedded displays. The TOUPLED also may be used in personal electronic device applications, such as near-eye head-up displays, in which the TOUPLED display device is integrated on to a head mounted apparatus such as a pair of eyeglasses, sunglasses or visor. Such devices may be utilized for virtual reality or augmented reality applications. In some implementations, the TOUPLED may be part of a very near-eye display, in which the TOUPLED display device is integrated on a curved surface intended for direct contact with the eye such as a contact lens. The TOUPLED device also may be used with personal desktop and laptop computer displays, portable electronics devices such as PDAs, cellular phones, digital music players, digital game players, GPS devices, and electronic readers.

0105The TOUPLED also may be used in photo-sensitive devices in which the TOUPLED transparent display pixel matrix is interlaced with photo-detectors on an integrated circuit, such as a Complimentary-Metal Oxide Semiconductor (CMOS) circuit. The TOUPLED also may be used in stereoscopic displays for three-dimensional viewing of electronic images. In a stereoscopic display, two images are created from a single TOUPLED display device. Each of the images is generated with spin-polarized TOUPLED pixels that emit pure, or nearly pure, helically polarized light. Such a system may require the viewer to wear eye-wear possessing polarized filtered lenses to permit each eye to perceive the two separate images generated by the display.

0106TOUPLEDs also may be used in dual-sided transparent display applications. In such displays, two TOUPLED devices are joined so that the respective optically active blocking layers of each device are adjacent to each other. Light is emitted from each device in opposing directions to create a display that is active on two sides that are opposite to each other. The TOUPLED also may be used for illuminating an area and in active electro-optical camouflage systems.

0107TOUPLED devices may be used for in-line-of-sight illumination for task lighting. For example, TOUPLEDs may be used in a head-mounted apparatus to provide head-mounted illumination. Because the TOUPLED is transparent and emits light from one side, the head-mounted apparatus may be mounted in the line of sight of the user such that the region in the line-of-sight of the user is illuminated while the user also views the region through the TOUPLED. TOUPLEDs also may be used in systems that use and/or provide visual feedback. For example, TOUPLED devices may be integrated on an industrial or medical boroscope lens, a microscope lens, and other inspection devices. TOUPLED devices also may be used with or integrated with cameras.

0108It is understood that other modifications are within the scope of the claims. For example, although red, blue, and green light-emitters are discussed above, other colors may be used.